The present invention relates generally to improvements in artificial ornamental stones and decorative objects and it relates more particularly to improved artificial stones exhibiting chatoyancy and being highly wear resistant.
A highly attractive gem stone is cats-eye, a chrysoberyl which possesses chatoyancy and other desirable characteristics when properly cut as a cabochon. There are many stones which exhibit chatoyancy to various degrees. However, the gem chrysoberyl cats-eye is characterized by two optical effects, which are not present together in other cats-eye gemstones other than the alexandrite variety of chrysoberyl. The first is the formation of bright, narrow line as a result of corresponding point sources of light at or near the plane perpendicular to the base of the stone. The second is the formation over part of the stone body of a bright area of a color such as light greenish yellow or light yellowish brown, with the rest of the body a darker color, such as dark yellowish brown or brown or greenish yellow. This is often referred to as the "milk-and-honey" effect. It is caused by the stone being illuminated by a broad source of light or by a point source of light from the side, at an angle close to parallel to the base of the stone. The dividing line between the light and dark portions shows as a brighter line, whose width and intensity is a function of the size of the source of illumination. The rarest of gem cats-eyes, the alexandrite cats-eye, is chrysoberyl with impurities including a chromium impurity which alter the color absorption spectrum of the body of the stone such that a red or red-purple color is seen by incandescent illumination and a green color is seen by natural daylight illumination.
With two point sources of illumination as the stone is rotated in a plane parallel to its base, the separation of the two bright lines will change from a maximum to zero and back to maximum, thus giving the appearance of closing and opening of an eye.
Many attempts have been made to produce artificial cats-eyes and similar and related gem stones but the results have been far from satisfactory. The artificial stones previously produced lack the attractive and rich appearances of the natural stones and the artificial nature thereof is clearly apparent. Moreover, the methods heretofore employed are of very limited application and are lacking in versatility and adaptability.
Another drawback of most artificial gem stones, as well as many natural gem stones, is their low scratch and abrasion resistance by reason of the softness of the stone. Many artificial stones are formed of glasses or other man-made materials having hardness between 4 and 6 on the Mohs scale and are thus easily scratched or abraded in ordinary wear and by many of the domestic abrasive cleaners.